If your main interest is airband. Then why not consider buying an antenna that is optimised for that.. An Airband antenna will work away from the airband, it's just it will be compromised away from airband. Discones, should give a better broadband coverage than a simple vertical.

Doesn't help - but my first discone I made myself in school in 1974 for my final metalwork project - mainly because they're mechanically simple, very robust, and just lots of repeating. Casting the two aluminium hubs, then drilling and tapping the holes, then spinning all the threads. A bit of paxolin for the insulator and a socket and one bit of wire. It lasted until my first house move in the late 80s, when it got left behind. I suppose this is why they're still expensive - just too many components and weight, plus the cost of the actual metal.

Thinking about it, apart from wind resistance, making a solid discone with modern materials would be pretty easy - why don't people do it?. I'm thinking of something like a cone made from plastic, covered in something conductive, then same with the disc? Kind of a lamp shade screwed to the N type, then a plate on the top araldited to the top of the N type with the pin soldered to the conductive stuff glued to a plastic plate or something. You can get very thin copper sheet.

If you used copper, it would also weather really nicely. Might be a bit flimsy for exposed conditions, but for a wall mount in a sheltered place, it could be a decent performing aerial, and if you don't need extended frequency coverage downwards, it wouldn't even be that big?